Such sensors are disclosed by way of example in DE 197 53 805 C2 and in the brochure “Temposonics Position Sensors”, 551019 A of the company MTS (www.mtssensors.com/fileadmin/media/pdfs/551019.pdf) and are in particular used in industrial metrology to measure positions, lengths or covered distances. The waveguide can be a thin bar, a wire or a pipe of a ferromagnetic material such as iron, nickel or cobalt which can have a length of a few centimeters up to a plurality of meters, for example. A so-called “position magnet”, for example in the form of a permanent magnet, which generates a magnetic field in the waveguide is typically attached to the component whose position should be detected. The position magnet can, for example, be of ring shape and surround the waveguide. If an electrical current pulse is sent through the waveguide, a further magnetic field which is variable with respect to time and place is generated in the environment of the waveguide in addition to the magnetic field generated by the position magnet. Due to the interaction of the two magnetic fields at the site of the position magnet, a mechanical pulse such as a longitudinal pulse and/or a torsion pulse can be generated in the waveguide and moves along the measurement path. A transducer of the position sensor typically serves to convert the mechanical pulses conducted by the waveguide into position signals. The transducer can, for example, comprise a coil or a piezoelectric measurement element. The transducer can, for example, be designed as described in EP 0 882 212 B1. The position of the position magnet can ultimately be determined by a measurement of the travel time of the mechanical pulse. Position sensors based on the magnetostrictive measurement principle work in a contactless manner and supply absolute values. They do not require a recalibration and they are also suitable for adverse conditions of use. They are frequently configured as linear path sensors. An application of such position sensors within hydraulic cylinders in order to detect their piston setting is described in DE 20 2006 012 815 U1, for example.
The described longitudinal pulses or torsion pulses move in the waveguide in both directions away from the position of the position magnet. At the one end of the waveguide, they are detected with the aid of the transducer in order to determine the current position of the position magnet along the waveguide using the described measurement of the travel time. At the other end, it has to be prevented as effectively as possible that the pulse is reflected and propagates back along the waveguide. This would interfere with the detection of the pulse propagating directly in the direction of the transducer or would make it ambiguous.
Elastomer sleeves are described in EP 0 882 212 B1 for this purpose and are plugged onto the end of the waveguide remote from the transducer. Elastomers having different properties can be plugged on after one another in order to adapt the damping effect. For example, a sleeve of a soft elastomer which keeps the reflection small can first be provided. It can be followed by sleeves of a harder elastomer having a greater damping. Such damping elements, however, require the expensive and complicated pushing of the sleeves onto waveguides which are as a rule configured as wires.
In other known solutions, an elastomer material is cast around the waveguide in a casting mold or is applied in an injection molding process, wherein a sleeve of an elastomer having homogenous properties is produced in the process.
A position sensor is disclosed in DE 197 53 805 C2 in which the waveguide is supported in a support of insulating material. On the assembly, a pressing sleeve is pressed onto the axial end region of the waveguide together with the insulating material.
DE 696 34 988 T2 discloses a waveguide suspension device for an acoustic converter, said device comprising a suspension sleeve and a damping element. The damping element has an inner sleeve and a pressure means for pressing together the inner sleeve and is arranged between the suspension sleeve and the remote end of the waveguide.